This invention relates to a fuse link, and more particularly to an integrated circuit fuse link and a method for making the integrated circuit fuse link.
Typically a integrated circuit fuse link consists of a conductive trace, made of metal or conductive polysilicon, that includes a fuse portion. The fuse portion is thinner or narrower than the rest of the trace, and thus experiences a higher current density. The fuse link is blown by subjecting the fuse link to a current pulse that heats the material of the fuse portion sufficiently to vaporize a gap in the fuse portion, creating an open circuit.
The present fuse links have generally performed adequately. One drawback, however, is that blowing the fuse links requires applying a relatively large current: Normally, to blow a fuse portion that is 3 to 4 micrometers wide requires applying a current pulse to the fuse link of from 300 to 500 milliamp. Another drawback is that applying a simple pulse sometimes only vaporizes a small gap in the fuse portion. The small gap opens the circuit, preventing the pulse from causing further heating, and thus from widening the gap. After the pulse is no longer applied to the fuse link, into the gap can settle conductive fragments of the vaporized fuse portion. In sufficient quantity, the fragments can bridge the gap. The bridge may suffice to repair the gap for the relatively small currents (e.g., 20 milliamps) to which the fuse link is subjected under normal operating conditions.
One approach to the problem of gap bridging is to create larger gaps. Presently larger gaps are created by changing the current applied to the fuse link from a simple pulse to a more complex waveform. The complex current waveform typically includes a slow ramping up to the maximum current. The more complex current waveform, however, takes longer to apply to each fuse link. Time is a consideration, since programming a fuse link EPROM may require blowing thousands of fuse links. The complex current waveform also requires complex equipment to generate.